The present invention relates to image-forming device and, more particularly, to an image-forming device having a patterned roller that is able to produce a unique, identifying mark on a document.
Devices used to form images, such as laser printers, inkjet printers, photocopiers, fax machines, and scanners, are well known in the art. Images are formed by these devices using various techniques. For example, in laser printers and photocopiers, a latent image is created on an insulating, photoconductive roller by selectively exposing portions of the photoconductive roller to light to form exposed and unexposed portions having different electrostatic charge densities. A visible image is formed using electrostatic toners that are selectively attracted to the exposed or unexposed portions depending on the charge of the photoconductive roller or the toner. A sheet of paper or other print medium having an electrostatic charge opposite to the charge on the toner is passed close to the photoconductive roller. The toner is transferred from the photoconductive roller to the paper, still in the pattern of the image developed from the photoconductive roller. A set of rollers melts and fixes the toner to the paper to produce the printed image.
Image-forming devices are used around the world to print, or otherwise image, documents. As the number of documents produced by these devices increases, it is becoming important to be able to trace or identify the device that produced a particular document. For example, law enforcement officials commonly need to trace a document to prove or disprove that a suspected printer or photocopier was used to produce the document.
Some countries require that imaged documents be traceable to the device that produced them. To provide this traceability, yellow toner has been used to print a serial number or other xe2x80x9cfingerprintxe2x80x9d on the document. While this technique allows the document to be traced, it requires firmware support to produce the yellow fingerprint, adding to the complexity of the firmware. In addition, this technique increases the consumption of yellow toner, thereby requiring the yellow toner to be replaced more often. Furthermore, the fingerprint interferes with or affects the quality of the image.
Another technique for tracing imaged documents is disclosed in U.S. Pat. No. 6,321,648 to Berson et al., which discloses a method of tagging sheets of recording material. The method comprises applying a random pattern to the recording material. The pattern is present on a roller of an image-forming device, such as a transport roller, and is imprinted or embossed onto the recording material.
A roller for use in a paper path of an image-forming device is disclosed. The roller comprises a purposeful pattern that is formed in an outer surface of the roller. The purposeful pattern is configured to form an identifying mark on a print medium that is transported along the paper path of the image-forming device. The purposeful pattern on the roller affects the amount of toner that is present on the print medium.
A method of producing an identifying mark on a print medium is also disclosed. The method comprises providing an image-forming device that has at least one roller having a purposeful pattern that affects an amount of toner present on the print medium. The print medium is advanced along the paper path and contacted with the roller to form the identifying mark, which is unique to the image-forming device.